Sound absorbing panels or liners often are used to form the inner barrels of the inlets of jet engine nacelles to attenuate noise generated by the engine's fan blades. Such panels or liners often include an acoustic cellular core disposed between a perforated inner skin, and an imperforate outer skin. The perforated inner skin permits sound waves to enter the innermost ends of the open cells of the core, and the imperforate outer skin reflects the sound waves. Such an arrangement is known to dissipate sound energy. Generally, the greater the open area of the perforated inner skin and the greater the number and volume of open cells in the acoustic cellular core available to receive sound waves through the perforated inner skin, the greater the sound attenuation capability of an acoustic inner barrel of a nacelle inlet.
Typically, an acoustic inner barrel of a nacelle includes a plurality of circumferential acoustic barrel segments or panels. When the segments are joined together along longitudinal seams, they form a complete acoustic inner barrel. Historically, the adjoining edges of the acoustic cellular cores of the segments have been connected by a foaming adhesive of a type known to persons of ordinary skill in the art. As shown in FIG. 1, the foaming adhesive 10 typically fills partial cells 12 along adjoined cut edges 14, 16 of the acoustic cellular core sections 18, 20. The foaming adhesive 10 also can at least partially fill adjacent full cells 26. The foaming adhesive 10 also typically blocks at least some openings 22 in the perforated inner skin 24 along the joint. Accordingly, the foaming adhesive 10 effectively prevents sound waves from passing through at least some of the openings 22 in the inner skin 24, and also prevents sound waves from entering the blocked and partially blocked cells 12, 26 of the core sections 18, 20. As a result, the sound attenuation capability of the associated acoustic inner barrel is less than it would be if the openings 22 and cells 12, 26 remained unblocked by the foaming adhesive 10.
Mechanical joints also have been used to connect adjoining edges of acoustic panels. As shown in FIG. 2, such a mechanical joint includes an inner plate 30 and an outer plate 32 on opposed sides of a longitudinal joint 34 between first and second portions 36, 38 of an acoustic barrel 40. A plurality of fasteners 42 extend thorough the barrel portions 36, 38 and the inner and outer plates 30, 32, and secure the barrel portions 36, 38 together. Unfortunately, the inner plate 30 necessarily blocks openings in the perforated inner skin 46, and prevents sound waves from entering the underlying cells 44. Therefore, like the foaming adhesive discussed above, the mechanical connection shown in FIG. 2 effectively reduces the available acoustic area of the inner barrel 40 that is available for sound attenuation.
Accordingly, there is a need for a joining method and system for connecting adjoined edges of acoustic cellular panels that minimizes the blockage of openings in the inner skin and of cells proximate to the joint. In addition, there is a need for such a joining method and system that provides a strong and durable connection between the acoustic panels or segments.